Method of treating alloys



Sept. 2 6, 1939. F. NoLL Er Al.

l METHOD OF 'I'REATING ALLOYS Filed Sept. 8, 1,9158` 3 Trearmnz 0 0 0 0 0 0 0 0 0 .M 0 0 0 0 0 W 9 M J 0 W INVENTORS d m z W m m F Patented Sept. 26, 1,939

UNITED STATE METHOD or TREATING AELoYs Franz Noll, Schonwalde, near Velten, Kreis Ost- Havelland, and Paul Germany, assignors Wolf, Berlin-Haselhorst, to Fides Gesellschaft.

fr die Verwaltung und Verwertung von gewerblichen Schutzrechten mit beschrnkter Haftung, Berlin, Germany, a corporation of Germany Application September 8, 1938, Serial No. 228,938 In Germany August 6, 1936 4 Claims.

This invention relates to the treating of alloys, and particularly to the method of treating ironaluminum alloys.

Iron-aluminum alloys having an aluminum content of more than 1.5% have beenheretofore considered as having too poor magnetic properties for satisfactory use in certain electrical apparatus andsystems. The permeability values of the untreated alloy are not of sufficient value and when employed in weak magnetizing fields are not sufficiently constant to justify their use.

An object of this invention is to provide for so treating iron-aluminum alloys as to impart thereto a relatively high initial permeability. -Another object of this invention is to provide a method of treating iron-aluminum alloys to give them a high initial permeability which is not so detrimentally affected when subjected to weak magn'etiaing fields as to prohibit their use.

Other objects of this invention will become apparent from the following description, when taken in conjunction with thesaccompanying drawing, in Which- Figure 1 is a graph illustrating the results obtained when an iron-aluminum alloy containing 4.6% aluminum is treated in accordance with the teachings of this invention, and

Fig. 2 is a graph illustrating the results obtained when an iron-aluminum alloy containing 7% of aluminum is similarly treated.

In practicing this invention, alloys consisting of more than 1.5% of aluminum and preferably from 1.5% to 8% of aluminum with the balance iron are initially cold worked as by rolling or drawing in an amount ranging from 25%to 85% and preferably from 50% to 70% into the size and shape of the desired finished article, such as wire, sheet or'ribbon, depending upon the use. In order to increase the initial permeability of the alloy, the cold worked alloy is then subjected to a heat treatment consisting of annealing it at a temperature ranging between 900 C. and 1100.C. in a preferred atmosphere, after which it is cooled in a preferred manner.

In annealing the cold worked alloy, it. has been found to be preferred to anneal it in the presence of oxygen as compared with other annealing atmospheres, such as hydrogen or illuminating gas or the like. Not only does the annealing in the presence of oxygen give higher initial permeability for the alloy, but when employed Within the range of weak magnetizing fields, it `is found that the permeability is more lconstant than the value obtained with other annealing atmospheres, the increase in the permeability over the initial permeability being much le'ss than that obtained with the other annealing atmospheres. 1

(Cl. 14K-12) The oxygen may be supplied to the annealing chamber in a number of different ways. In practice, it has been found desirable to sometimes supply it in the form of a material, such as pyrolusite (MnOz), which has the property of liberating oxygen when heated. If desired, the oxylgen may be supplied to the annealing chamber by continuously supplying air thereto. In all cases, it is desired to limit the oxygen content and maintain it so low as to not formscale on the alloy during the heat treatment thereof, In

order to insure against such formation oi scale,

iron shavings may be mixed with the oxygen 'liberating material, or where `only air is employed as the annealing atmosphere, the alloy may be embedded in clean steel or iron shavings. After having subjected the alloys to the annealing temperature in the presence of oxygen, the alloys are so slowly cooled that a period of time of at least one hour is necessary to lower the temperature from theannealing temperature down to 400 C. In some cases, a cooling rate in which a period of time of four hours is necessary to lower the temperature to about 200 C. is to be preferred.

By way of example, in order to illustrate the improved initial permeability values obtained by annealing the iron-aluminum alloys in oxygen in accordance with the teachings of this invention, and also to illustrate the relative increase in permeability of the same alloys when employed within the range of weak magnetizing fields, reference may be had to the following.

table in which the increase in permeability is given in percentage. f

Initial Increase in pcrmepermeabilabxhty ity, percent Annealng conditions Air supplied to furnace The values given in the foregoing table are obtained when an alloy, containing 3.68% of aluminum with the remainder iron, is cold rolled into the final shape of a ribbon having a thickness of 0.1 mm., annealed for one hour at a temperature of 950 C. under the annealing conditions indicated in the table, ;fand then slowly cooled in the furnace at such a rate as to require a period -of time of four hours to reduce the temperature to 200 C. In referring to the table, it is evident that where the iron-aluminum alloys are annealed in oxygen either as liberated from a material such as pyrolusite or by continuously supplying air to the furnace, the initial permeability obtained is far greater than that obtained where hydrogen or nitrogen is employed, as the annealing atmosphere. Further, the relative increase in permeability for an increase in field strength from up to 0.1 oersteds is so small for the alloy annealed in the presence of oxygen as to not be objectionable.

Referring to Figs. 1 and 2 of the drawing, the results obtained by following the teachings of this invention are illustrated with reference to the initial permeability and the rate of increase in initial permeability for ribbons of iron-aluminum alloys having three diiferent thicknesses of 0.1, 0.2 and 0.3 mm., respectively, when sub- -jected to different treatments. In both figures, the values of the initial permeability ar indicated by the marked points located on the solid connecting curv and the values of the quantity representing the rate of increase of the initial permeability in percent are indicated by the marked points located on the dotted connecting curves. In both gures, the numbers appearing along the axes of the abscissae of the graphs indicate the treatments to which the alloys were subjected, as will be described hereinafter..

The curves of Fig. 1 represent the results yobtained from an alloy containing 4.6% of aluminum, while those of Fig. 2 represent the results obtained when treating an iron-aluminum alloy containing 7% of aluminum. In all cases, the alloys were coldworked about 60% to the final ilnished size and were then annealed for onehalf hour at a temperature of 910 C. in the atmospheres as described hereinafter and slowly cooled. For comparative purposes, different annealing atmospheres were employed.

Taking the annealing atmosphere treatment in the order which it appears along the abscissae of both Figs. 1 and 2, treatment I consists'in annealing. the iron-aluminum alloys in illuminating gas and cooling them in air; treatments land 3 consist in annealing the alloys in hydrogen and cooling themin water and in air, respectively; treatment I consists in annealing the alloys in illuminating gas and cooling them n slowly in the furnace; treatment 5 consists in annealing the alloys in the presence of a material which liberates oxygen and cooling them slowly in the furnace; treatment 6 consists in annealing the alloys while continuously supplying air to the furnace and then cooling them in air; and treatment 1 consists in annealing the alloys in the presence of pyrolusite and cooling them slowly in the furnace. i

In Fig. 1, curve I0 illustrates the initial permeability obtained for the alloy containing 4.6%

oi' aluminum and having a thickness of 0.1 mm., while curve I2 illustrates the increase in percent in the initial permeability for the same alloy. Curves Il and I6 respectively illustrate similar values for the same alloy having a thickness of L.02 mm. and curves Il and 2l respectively illustrate similar results for the same alloy having a thickness of 0.3 mm. In Fig. 2, the initial permeability of an alloy containing 7% of aluminum and having a thickness of 0.1 mm. is illustrated by curve 22, while the increase in percent in the initial permeability for the same alloy is illustrated by curve 24. Curves 270 land-@Irespcctively illustrate similar values for the same alloy having a thickness of 0.2 while curves .and 32 respectively are illustrative of results ob-v tained for the same alloy having .a thickness of Frntheaeremluitilevldentthatwherethe alloy is annealed in the presence of oxygen, much more favorable values of initial permeability are obtained while the increase of the initial permeability corresponding to an increase in fieldstrength of from 0 up to 0.1 oersteds is much lower than that obtained where non-oxidizing annealing atmospheres are employed. Alloys treated in accordance with this invention are satisfactory for use as protective sheaths of communication cables that are exposed to interference by power circuit currents and for shielding purposes in cases where the transient-distortion damping in telephone 'circuits must be increased. Further, in addition to many other uses, they can be used equally well in those cases, such as in repeaters, where the material must have, in addition to a relatively high initial permeability, a permeability that remains substantially constant within very close limits in weak magnetizing elds,

Although this invention has been described with reference to a particular embodiment thereof, it is, of course, not to be limited thereto, except insofar as is necessitated by the prior art and the scope of the appended claims.

We claimas our invention: I

1. The method of treating iron-aluminum alloys containing from about 1.5% up to 8% of aluminum to impart thereto a high initialpermeability and improve the rconstancy thereof when subjected to weak magnetizing forces comprising. subjecting the alloy to cold work' in an amount ranging from 25% tb 85%, annealing thev cold worked alloy at a temperature between 900 C. and 1100 C. in the presence of oxygen, and slowly cooling the annealed alloy,

2. The method of treating iron-aluminum al- V loys 'containing from about 1.5% up to 8% of aluminum to impart thereto a high initial permeability and improve the constancy thereof when subjected to weak magnetizing forces comprising, subjecting the alloy to cold work in an amount ranging from 25% to 85%, annealing the cold worked alloy at a temperature between 900 C. and 1100" C. in the presence of oxygen, and slowly cooling the annealed alloy to a temperature of about 400 C. in the presence of oxygen.

3. The method of treating iron-aluminum alloys containing from about 1.5% up to 8% of aluminum to impart thereto a high initial permeability and improve the constancy thereof when subjected to'weak magnetizing forces comprising, subjecting the alloy to cold work in an amount ranging from to '10%, annealing the cold worked alloy in air at a temperature between 900 C. and 1l00 C., and so cooling the alloy from the annealing temperature that the temperature is reduced to about 200 C. in a period of time of about four hours.

4. The method of treating iron-aluminum alloys containing from about 1.5% up to 8% of aluminum to impart thereto a high initial permeability' and, improve the constancy thereof when subjected to weak magnetizing forces comprising, cold workingv the alloy to defcrm it an amount ranging from 50% to 70%, annealing the alloy at a temperature between 900 C. and 1100" C. in the presence o f a material which liberates "oxygen, the oxygen content of `the material being so low that the annealed alloy is free from scale, and cooling the alloy to a temperature of 

